Insulated oak door – Barn Door

Last month’s article explained the battles we had to satisfy the local council’s Conservation Officer, and described the beginning of the door’s construction. Here’s the concluding episode

Insulated oak door - Barn Door Photo

The first stage of this project gave me two identical frames for the door itself. From now on they would be treated completely differently, so I put one to one side and concentrated on the internal frame.

The first step was to cut a 6mm slot round the inside edge of the frame components to house the plywood panels. Once the ply had been cut to size the frame was glued together, photo 1. I then planed a small chamfer off the inside edge of the frame and cut out a hole in the central rail for the letterbox.

Fitting the inner boards

Next I machined up the vertical boards and fitted them loosely in place, using spacers to ensure that there was a 2mm gap between them, photo 2. Once I was happy with the fit, I removed the boards and gave the edges a coat of Polyx oil, completely covering the tongues and grooves as this area would be difficult to finish properly once the door was assembled.

Barn Door Instruction Insulated oak door Photo 1-6

I then marked the centre point of each board on a slim batten to use as a guide rod. The boards were then clamped in position and the door was tipped on its side so I could screw each board in place from the inside, photo 3, using the rod I had previously marked as a positional guide. I screwed down only one edge of each board to allow the wood to move in the future. All that remained was to cut the letterbox slot through the boards, photo 4.

The external door frame

Now it was time to go back to the external frame. I started by gluing it all together, photo 5, and then cut the slot in the centre rail for the letterbox.

The next job was to loosely fit the vertical boards which I had previously machined to size when I made the inner frame. Note that the middle board has been tongued on both edges, photo 6, and so needs to be wider than the other boards by the depth of the tongue if they are all to be the same finished size.

The three middle boards now needed to be cut in two, and to have tongues and grooves cut in the ends, photo 7. Note that I’ve also cut some shallow stress-relieving grooves on their back faces. The two outer boards run the full length of the door; the three middle boards are cut to overlap the centre rail, photo 8. This is then tongued and grooved on all four edges and slid into place, photo 9.

Insulated oak door Barn Door Instruction Photo 7-12

Finishing the frame

After fitting the bottom three boards loosely in place, photo 10, I marked the letterbox position on the outer middle rail, took the door apart again, chamfered the inside edge and cut out the letterbox opening.

With the frame in pieces, I gave all the edges – which will be difficult to finish after the door is assembled – a coat of Sikkens HLS Plus and allowed this to dry before reassembling the frame.

I started with the top panel and the centre rail, photo 11. The two parts of the middle rail were glued together; the other boards are left free to move. Note that the exposed middle rail only runs the width of three boards. Its purpose is to allow a waterproof joint around the letterbox. Without this, water would track down the grooves and run into the letterbox opening. The door is to have a particularly large letterbox which will completely cover the rail when it’s fitted.

Finally, I fitted and clamped the lower boards in place before screwing them down to their rails using stainless steel screws, photo 12. Then I checked that the letterbox fitted within the opening without binding, photo 13, and neatened up the cut edges

Draught seals and locks

To draught-seal the bottom edge of the door, I chose to fit a Norseal automatic threshold seal. This is mortised into the bottom of the door, but while the door is in two halves it’s an easy job to rebate the bottom of both frames to house the seal, photo 14. I also routed out a recess in the two stiles to house the mortise lock before sanding the internal faces of the two frames smooth, photo 15.

Adding insulation

Next, I fitted 20mm thick Celotex insulation into the recesses created in the frames. Note that I’ve covered all the cut edges of the Celotex with aluminium tape, photo 16, to ensure that the wood glue didn’t get onto the foam core of the Celotex. Some plastics react badly when they touch, and although in theory polyurethane wood glue shouldn’t react adversely with the Celotex foam, this precaution ensures that I won’t have a problem in the future.

I then test-fitted the two frames together before giving both inner faces a thin coat of polyurethane adhesive, photo 17. At last I was able to bring the two frames together, photo 18, working on my bench which I know is flat. It was vital to glue it up on a perfectly flat surface, as any discrepancy would otherwise be locked in for life.

Barn Oak Door Instruction Photo 13-18

Fitting and finishing

Once the glue had cured I carefully cleaned the dried excess off, trimmed the door to its final size, rebated it for hinges and temporarily fitted the door into the frame. This allowed me to finish the door, inside with Polyx oil and outside with Sikkens ebony woodstain, as required by the Conservation Officer.

All that was left was to fit the door and frame, attach the door furniture and lock, and add the seals to the door frame for the job to be finally finished.

A job well done

Insulated oak door - Barn Door PhotoThe door has been fitted for a while now, and it has performed remarkably well in a wide range of weather conditions. When the sun shines on the black exterior, the outside of the door can get blisteringly hot. On the inside, however, the door doesn’t even get warm, which bodes well for its long-term thermal performance.

My only disappointment is that the door doesn’t look as spectacular as I would have liked, especially after all this work; in fact no one even seems to notice that we have changed the door. However, from a conservation point of view that is exactly what was wanted, so I suppose it’s a job well done!

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